Enhanced geothermal systems (EGS) using CO2 as working fluid - A novelapproach for renewable energy with simultaneous sequestration of carbon

Responding to the need to reduce atmospheric emissions of carbon dioxide, Donald Brown (2000) proposed a novel enhanced geothermal systems (EGS) concept that would use COsub 2 instead of water as heat transmission fluid, and would achieve geologic sequestration of COsub 2 as an ancillary benefit. Following up on his suggestion, we have evaluated thermophysical properties and performed numerical simulations to explore the fluid dynamics and heat transfer issues in an engineered geothermal reservoir that would be operated with COsub 2. We find that COsub 2 is superior to water in its ability to mine heat from hot fractured rock. COsub 2 also has certain advantages with respect to wellbore hydraulics, where larger compressibility and expansivity as compared to water would increase buoyancy forces and would reduce the parasitic power consumption of the fluid circulation system. While the thermal and hydraulic aspects of a COsub 2-EGS system look promising, major uncertainties remain with regard to chemical interactions between fluids and rocks. An EGS system running on COsub 2 has sufficiently attractive features to warrant further investigation.